Deleting tuples using separate transaction identifier storage

ABSTRACT

Data from a database object are processed. Transaction information for a set of data of the database object is stored separate from the set of data in an allocated storage space, where the transaction information indicates visibility of the set of data to other transactions. A map structure is generated indicating storage of the set of data and the allocated storage space of the transaction information. The transaction information is altered in response to a transaction to the set of data to alter visibility of the set of data. Altering the transaction information is accomplished by providing updated transaction information within a new storage space in accordance with the transaction to the set of data and generating a descriptor for the transaction indicating an existing location of the set of data and the new storage space.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/501,745, entitled “DELETING TUPLES USING SEPARATE TRANSACTIONIDENTIFIER STORAGE” and filed Sep. 30, 2014, the disclosure of which isincorporated herein by reference in its entirety.

BACKGROUND

Present invention embodiments relate to deleting tuples in a database,and more specifically, to deleting tuples in a database column storewhen the database employs separate transaction identifier storage.

In a relational database, tables of data are stored in which data fromone table may have some relationship with the data stored in anothertable. The relationships between the data in the various tables allowthe processing of queries (e.g., database searches) in an orderlyfashion.

When plural users or computer processes have access to the same databasesimultaneously (i.e., concurrently), issues may arise with respect tochanging the existing data in the database. For example, if a databaserecord is in the process of being created or modified, many databasesystems that do not provide concurrency control will “lock” that recordfor the duration of the update. Thus, in order to avoid the “locking” ofindividual or groups of records, multiple copies of the same record arepermitted using multi-version concurrency control (MVCC) wherebymultiple transactional changes to a database record are reconciled atsome later point in time. However, when a database employs MVCC,multiple users or processes may change a record and multiple copies ofthe same record (with their corresponding changes) are stored until allchanges are reconciled and committed.

Thus, in order to reconcile multiple changes to a given record,transaction identifiers (TIDs) are maintained for each copy or versionof a record with actual or attempted record changes.

A version of a record is marked for removal, either due to deletion orupdate of the record, by modifying the TID associated with that record.The TIDs may be modified “in place”; the record is read, then modified,and stored anew, thereby undesirably increasing database input/output(I/O) volume. Furthermore, these TIDs cannot be compressed: the modifiedTID may not fit in the space allowed for the original TID. As a result,in many cases, the storage volume of the table data is actually smallerthan the storage volume of the TIDs.

SUMMARY

According to one embodiment of the present invention, data from adatabase object are processed. Transaction information for a set of dataof the database object is stored separate from the set of data in anallocated storage space, where the transaction information indicatesvisibility of the set of data to other transactions. A map structure isgenerated indicating storage of the set of data and the allocatedstorage space of the transaction information. The transactioninformation is altered in response to a transaction to the set of datato alter visibility of the set of data, where altering the transactioninformation includes: providing updated transaction information within anew storage space in accordance with the transaction to the set of data;and generating a descriptor for the transaction indicating an existinglocation of the set of data and the new storage space. The map structuremay be updated to include the generated descriptor or a pointer thereto.

Embodiments of the present invention include a method, system andcomputer program product for deleting tuples in a database using aseparate transaction identifier storage scheme in substantially the samemanner described above.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Generally, like reference numerals in the various figures are utilizedto designate like components.

FIG. 1 is a diagrammatic illustration of an example computingenvironment for use with an embodiment of the present invention.

FIG. 2 is a graphical illustration of a zone index data structure anddata in several stages of transition when managing tuples in a databaseaccording to an embodiment of the present invention.

FIG. 3 is a procedural flow chart illustrating a manner in which tuplesare added, modified or deleted in a database according to an embodimentof the present invention.

FIG. 4 is a procedural flow chart illustrating a manner in which tuplesare deleted in a database according to an embodiment of the presentinvention.

FIG. 5 is a procedural flow chart illustrating a manner in which tuplesare added in a database according to an embodiment of the presentinvention.

FIG. 6 is a procedural flow chart illustrating a manner in which added,modified or deleted tuples in a database are processed during a databasecommit according to an embodiment of the present invention.

DETAILED DESCRIPTION

Present invention embodiments improve optimization of a search engine(e.g., a database search engine) operation by storing transactionmetadata separately from the data and/or other metadata. In one example,the transaction metadata includes transaction identifiers (TIDs). TheTIDs may be based on an integer counter that increments monotonically(e.g., by one) for each new transaction or database scan, therebycreating a unique ID for each transaction. Briefly, the TIDs may beassigned as creator TIDs (ctids) that are unique for a given record ortuple that is newly created by the transaction, or as deleter TIDs(dtids) that are unique for a given record or tuple that is to bedeleted (or changed) by the transaction. The ctids and dtids are storedin a column store with one or more TIDs (creator or deleter) beingassociated with a given tuple. This technique allows several versions ofa tuple to exist, where different TIDs may be associated with theversions of a given tuple.

Plural tuples may be grouped together to form a database zone. The zonemay comprise sections or segments of a given table, or may be formed ofdata partitions of convenient size for data processing. Zone indices aremaintained along with or that include zone maps that may, in turn,include other indices or descriptors such that a descriptor entrydescribes the storage for a set of tuples (i.e., the zone index providesa map structure that includes indices, descriptor or other datapointers). A zone index may include one descriptor entry with oneversion of the dtid column for a set of tuples, and may include anotherdescriptor entry that describes the storage for the same set of tuples,yet with a different version of the dtid column. The zone indices areimplemented such that a given transaction can determine which of theversions of the dtid column it should use when processing the set oftuples. Zone indices are further described below.

For example, metadata may be maintained about each region of tablestorage. The metadata may contain value ranges or range maps thatindicate minimum (min) and maximum (max) values for data of a givencolumn (col) (e.g., the min/max values among individual column valuesstored in a database cell). A zone map may contain multiple range maps.

For example, if a storage region is known to contain records with columnvalues between 100 and 200 (i.e., col 1 {100, 200}), then a queryrestricted to records with column values greater than 500 will not readthat storage region. In contrast, an index provides a pointer to arecord (e.g., column value) with a specific value. When the columnvalues associated with a given index are sorted, then an index mayprovide a starting or stopping point for a search. When range maps areemployed, record addition and deletion may not require a change in therange map as long as those record's column values fall within the rangemap. The zone map may include both indices and range maps, as describedhereinafter.

The techniques of present invention embodiments provide multipleadvantages. For example, when rows are deleted, the only data written isa new version of the dtid column. Since a change to the dtid columncreates an entire new version of the dtid column that is stored in newstorage area, the dtid columns can be compressed. If many entries areaffected by a deleting transaction, any new versions of the dtid columnsmay be buffered and processed out sequentially, thereby furtherminimizing any I/O costs. Multiple entries for the same tuple set cancoexist with visibility of the tuple for processing being controlled bythe zone index. For example, the zone index comprises information suchthat a given transaction “sees” those tuples that are appropriate forthat transaction. The visibility control information allows databasescanners (e.g., accessing and/or retrieving database data) to operate inparallel with a deleting transaction and without synchronizing access tothe data. In addition, there is no vulnerability to “torn” or corruptedpage data during a read-modify-write sequence, because the deleteoperation creates a new version of the dtid in storage. In this regard,a database scanner “scans” data (e.g., zone metadata) to determine whichsegments or portions (e.g., zones) of the data are affected by one ormore transactions (i.e., plural transactions may be aggregated orcombined, when it may be more efficient).

In one example, the database scanner (e.g., a transaction processingmodule) may operate to access or retrieve data as follows. The scannerlocks the zone index with a shared lock, thereby allowing other scannersto operate in parallel (i.e., concurrently). The scanner creates a listof all zones (e.g., by zone identifier) that it intends to scan. Thescanner does not include any zones marked as deleted (e.g., garbagezones). The scanner allocates a scan version number to the scan byincrementing the scan version number associated with a given zone index,and adds that scan version number to the list of active scanners. Whenthe scan completes, the scanner removes the scan version number from theactive scanner list and computes the current oldest active scan versionnumber. If there are lists of entries (e.g., tuples) to be deleted thathave version numbers less than the oldest scan version number, then thescanner removes those entries.

An example environment for use with present invention embodiments isillustrated in FIG. 1. Specifically, the environment includes one ormore server or host systems 10, and one or more data servers 14. Hostsystems 10 and data servers 14 may be remote from each other andcommunicate over a network 12. The network may be implemented by anynumber of any suitable communications media (e.g., wide area network(WAN), local area network (LAN), Internet, intranet, etc.).Alternatively, host systems 10 and data servers 14 may be local to eachother, and communicate via any appropriate local communication medium(e.g., local area network (LAN), data center network, hardwire, wirelesslink, intranet, etc.). One or more clients or end user systems 30 may becoupled to host systems 10 via a network 40, or by a data center networkor data center edge switch.

Host systems 10, data servers 14, and clients 30 may be implemented byany conventional or other computer systems preferably equipped with adisplay or monitor (not shown), a base (e.g., including at least oneprocessor 15, one or more memories 35 and/or internal or externalnetwork interfaces or communications devices 25 (e.g., modem, networkcards, etc.), optional input devices (e.g., a keyboard, mouse or otherinput device), and any commercially available and custom software (e.g.,server/communications software, mapping module, transaction module,browser/interface software, etc.). Data servers 14 may comprise computeand storage nodes or database engine blades (e.g., in a datacenter orserver farm).

Data servers 14 may receive user/DBMS query or transaction informationrelated to desired database information (e.g., data, documents, etc.)from host systems 10. In another example, the transaction informationand queries may be received by the data servers, either directly orindirectly (e.g., from a client system). The host systems 10 may includea mapping module 16 to generate zone indices and/or zone maps for acolumn store (e.g., data range maps, ctids and dtids). In general, ctidsare unique identifiers assigned to a tuple upon tuple creation, whiledtids are unique identifiers assigned to a tuple upon tuple deletion,modification or replacement. The host systems 10 may also include atransaction module 20 to process transactions configured to add, modifyor delete tuples using the zone indices and/or maps.

One or more components of the host systems 10, network 12 and dataservers 14 may comprise a database management system (DBMS) or database18. The database system 18 may use any conventional or other database,or storage unit. Other DBMS components may be local to or remote fromhost systems 10 and data servers 14, and may communicate via anyappropriate communication medium such as network 12 and/or network 40(e.g., local area network (LAN), wide area network (WAN), Internet,hardwire, wireless link, intranet, etc.). Any clients, hosts, or dataservers may present a graphical user interface (e.g., GUI, etc.) orother interface (e.g., command line prompts, menu screens, etc.) tosolicit information from users pertaining to zone indices and maps, andtransactions, and to provide results (e.g., transaction results, storagestatistics, garbage collection statistics, etc.). Further, these systemsmay provide reports to the user via the display or a printer, or maysend the results or reports to another device/system for presenting tothe user.

Alternatively, one or more hosts 10 or clients 30 may generate zoneindices and/or maps and perform query processing when operating as astand-alone unit (i.e., without using data servers 14). In a stand-alonemode of operation, the host/client stores or has access to the data(e.g., zone indices and/or maps, databases, etc.), and includes mappingmodule 16 to generate zone indices and/or maps and transaction module 20to process transactions. The graphical user interface (e.g., GUI, etc.)or other interface (e.g., command line prompts, menu screens, etc.)solicits information from a corresponding user pertaining totransactions, and may provide reports (e.g., transaction results,storage statistics, garbage collection statistics, etc.).

Mapping module 16 and transaction module 20 may include one or moremodules or units to perform the various functions of present inventionembodiments described below. The various modules (e.g., mapping module,transaction module, etc.) may be implemented by any combination of anyquantity of software and/or hardware modules or units, and may residewithin memory 35 of the host and/or data servers for execution byprocessor 15. It should be understood, that the computing environmentdepicted in FIG. 1 provides example platforms (e.g., host systems 10,backend or data servers 14) for illustrating the techniques describedherein. In this regard, data and zone indices and/or maps on one dataserver 14 may have no relationship with data, and indices and/or zonemaps on another data server 14.

To facilitate the understanding of the inventive concepts presentedherein, a series of graphical illustrations, each representing anexample data structure for zone indices and their associated data, aredescribed with respect to FIG. 2. In general, present inventionembodiments relate to zone indices and zone maps, commit transactionprocessing, and the operation of database scanners for executingdatabase transactions. Associated with the zone index is a set of datastructures that may include: a read-write lock (e.g., in a pthreadimplementation) for controlling concurrent access to those datastructures such as descriptors, a monotonically increasing scan versionnumber, a list of the version numbers of active scanners, and a list,ordered by scan version number, of entries (e.g., zones) in the indexthat are waiting to be processed (e.g., deleted). In general, thetechniques described herein are made with respect to an iteration of adatabase scan or transaction.

As described above, the table data may be divided into zones eachcomprising some number of tuples. Each zone has a unique identifier,i.e., a zone identifier (ID). The zone ID is used to map, via the zoneindex, to a zone descriptor for that zone. In this example, three zonedata structures 21, 22 and 23 are depicted in accordance with thepassage of time, e.g., during processing of a transaction or scan.

A first data structure 21 is a starting point and comprises a given zoneID 200. The zone ID 200 is, in turn, associated with a zone index 210,where the zone index 210 has a pointer to a zone descriptor 220 (e.g.,with an example value of 37). Zone descriptor 220, in turn, comprisesdata pointers 222, 224, 226 and 228 (e.g., metadata associated with thezone) with each data pointer pointing to columns of data 232, 234, 236and 238 within the zone. Accordingly, the zone map includes the zoneindex and the zone descriptor, and the data structure 21 furtherincludes the underlying or associated data. In this example, zonedescriptor 220 has a dtid pointer 222, a ctid pointer 224, and pointers226, 228 to data stored for columns A and B, respectively. The data forthe dtid, the ctid, column A and column B may be stored separately fromzone descriptor 220. In this example, data structure 21 shows a zone mapand data for one zone of a table containing tuples with identifiersranging from 2000 through 2999.

At some point in time, a delete request is received or generated by theDBMS or record management system. The request may include a “deletetuple” request that includes a tuple identifier value, e.g., “2120”, inorder to delete tuple 2120 within the tuple identifier range of 2000through 2999. In a database that employs MVCC or other versioningscheme, multiple copies of the same or similar record (with theircorresponding changes) are stored until all changes are reconciled andcommitted. Accordingly, multiple unreconciled copies (versions) of atuple may exist, each with a dtid that corresponds to a time of thechange (e.g., either by a timestamp or driven by the sequentialincrementing of TIDs that inherently provide a time sequence).

Referring to data structure 22, in order to process the deletion oftuple 2120, a copy of the dtid column 232 is copied (or instantiated) asdenoted as dtid′ (prime) 242. The dtid′ column is modified to indicatethat tuple 2120 is to be deleted. For example, the current TID isinserted into the dtid′ column for tuple 2120 (e.g., to replace a NULLvalue or other deleter TID). In addition, tuple 2120 may be explicitlymarked for deletion in the column store metadata. Simultaneously, ornearly so, with the creation of dtid′ 242, a new zone descriptor 240 iscreated with an example value 42. The new zone descriptor 240substitutes the pointer 222 to the dtid column store with a pointer 252to the dtid′ column store as shown in the figure.

Upon a successful “commit,” some or all or the pending actions (e.g.,tuple additions, modifications or deletions) for the zone are finalized.Referring to data structure 23, after a successful commit, the zonedescriptor 220 and the dtid column store 232 are discarded or otherwisemarked for deletion as indicted by the arrowed “X” in the figure, thezone index is updated to point to zone descriptor 240, and the new zonedescriptor 240 refers to dtid′ 242 via pointer 252. In this regard, themetadata such as zone indices and zone descriptors may be stored involatile memory while dtid columns, ctid columns, and column stores Aand B may be stored in persistent storage. In addition, certaininformation may be held in a log file to facilitate databasereconstruction should a system failure or rollback occur. In thismanner, the zone index can use the various versions of the TIDs in thedtid columns to control the “visibility” of a given tuple to a giventransaction. The concept of tuple visibility is described with respectto the remaining figures.

A manner in which mapping module 16 and transaction module 20 (e.g., viaa host system 10, client systems 30 and/or data server 14) process datawithin a database object according to an embodiment of the presentinvention is illustrated in FIG. 3. Initially, given at step 310, arelational database comprises a plurality of tuples in a relation, wherea first set of tuple create TIDs and a first set of tuple delete TIDsare stored in a column store. Generally, the techniques described hereinare made with respect to databases that employ MVCC. However, anydatabase that allows tuple access, without strict record lockingmechanisms may employ the techniques described herein. Furthermore,those skilled in the art would realize that these techniques may beimplemented in a row store or hybrid store (e.g., a combination or rowand column stores) by separately storing certain deleter information inorder to achieve the compression and I/O efficiencies, etc., describedabove.

A transaction request is received that includes instructions to add,delete or modify tuples in a relation (or zone partition or segment) andthe transaction request is assigned a current TID at step 320. The tuplesets for the operation (i.e., those tuples impacted by the operation)are identified at step 330. The transactions, as used herein, may beexecuted by functions, function calls, procedures, remote procedurecalls (RPCs), and the like (e.g., by mapping module 16 and transactionmodule 20). For add transactions, the set of tuples to be added, or therepresentations thereof, may be referred to as an add-tuple-set. The addtuple transaction may include, e.g., actual tuple data, pointers to thedata, or tuple identifiers. For delete transactions, there is adelete-tuple-set provided in the request that identifies tuples to bedeleted. In this regard, for a delete transaction, tuples may be markedfor deletion. However, for simplicity, with a modify transaction, thetuples to be modified may be both modified and stored anew, while theoriginal tuples are deleted. In that sense, tuple modify transactionscomprise both an add-tuple-set to add modified tuples as a new set oftuples and a delete-tuple-set to discard the version of tuples prior tosaid modification.

Since a delete or modify transaction implies the removal of data, thedelete-tuple-set may be identified by querying the relation and applyingMVCC filtering (i.e., determining if a tuple is visible to thetransaction). It is determined whether a delete-tuple-set is part of thetransaction request (e.g., for delete or modify transaction requests) atstep 340. When the processing of a transaction request indicates that adelete-tuple-set is present at step 340, the process proceeds to step360 where the process description continues with respect to FIG. 4.Otherwise the process determines whether an add-tuple-set is present atstep 350. When a transaction includes an add-tuple-set, the processproceeds to step 370 where the process description continues withrespect to FIG. 5. When transaction processing for a given transaction(or set of transactions) is complete the process ends at step 380.

In the examples presented herein with respect to the various flowcharts,it will be appreciated that DBMS operations are complex, nested or mayotherwise comprise entry or exit points for the various enumeratedflowchart steps or other process steps that are not specificallydescribed or enumerated herein. Any given step or processing point mayinclude processing options for commit processing that may be initiatedat a convenient database processing point, e.g., a commit may beinitiated after any given transaction has been processed. Examples ofcommit processing are described in connection with FIG. 6.

Referring to FIG. 4, the manner in which mapping module 16 and/ortransaction module 20 delete tuples within a database object (e.g., atable or relation) continues from FIG. 3 to FIG. 4 as indicated byoff-page connector at reference numeral 410. In this example, thedelete-tuple-set is generated and comprises a hierarchy that may includea list of zones containing tuples to be deleted, and for each zone, alist of the tuples in that zone to be deleted at step 420. For each zoneassociated with tuples in the delete-tuple-set, a series of steps aredescribed with respect to each zone to be processed beginning at step430. The series of steps at 430 may be iteratively processed for eachzone, e.g., by way of a processing queue. With respect to each zone tobe processed at step 430, first and second zone descriptors, and firstand second dtids are referred to with respect to FIG. 4 in order toindicate a temporal relationship between the descriptors and dtids on aper zone processing basis.

A copy of a first zone descriptor is created to produce a second zonedescriptor at step 440. Further, a copy of the first zone's dtid columnis created to produce a second dtid column at step 445. The copy of thesecond zone descriptor is modified to describe the second dtid column atstep 450. For those tuples to be deleted in the zone, store the currentTID in the second dtid column at step 455. Garbage collection statisticsare computed (or generated) for the zone during zone processing and thegarbage collection statistics are stored in or along with the secondzone descriptor at step 460. Once the garbage collection statistics(e.g., additional metadata) are amassed for the given zone, the processat step 430 iterates until processing for each zone of thedelete-tuple-set is complete at step 470. The process returns, at step480, to FIG. 3 at step 350.

Returning to FIG. 3, it is determined whether an add-tuple-set is partof the transaction request (e.g., for add or modify transactionrequests) at step 350. When a transaction that includes an add-tuple-setis present, the process proceeds to step 370 where the processdescription continues with respect to FIG. 5. When the processing of atransaction request indicates that an add-tuple-set is not present, theprocess ends at step 380.

Referring to FIG. 5, the manner in which mapping module 16 and/ortransaction module 20 processes or accesses data within a databaseobject continues from FIG. 3 to FIG. 5 as indicated by off-pageconnector at reference numeral 510. In this example, the add-tuple-setcomprises a list of tuples or their identifiers. The tuples identifiedin the add-tuple-set are partitioned among their respective zones atstep 520. In other words, the tuples in the add-tuple-set may spanplural zones whereby the zoned tuple partitions are iterativelyprocessed on a zone-by-zone basis that is similar to the processing oftuples in a delete-tuple-set.

Each set of tuples assigned to a particular zone at step 520 aredecomposed into columns for their respective zones at step 530. Thedecomposing step 530 recognizes that for column stores of the presentinvention embodiments, column data has a correlation with tuple (row)data. As part of decomposing step 530, for all tuples added, theircorresponding ctid values are assigned or set to the current TID valuesince they are newly being created. Zone descriptors are created foreach zone with tuples added thereto, and their corresponding garbagecollection statistics for the new tuples may be set to a non-descriptvalue or NULL at step 540 (i.e., no database garbage exists for newlyadded tuples). When transaction processing for an add-tuple-settransaction (or set of transactions) is complete, the process returns,at step 550, to FIG. 3, step 380 where tuple processing ends.

In one example, once a portion of tuple processing with respect toadd-tuple-set and/or delete-tuple-set transactions are complete, acommit procedure may be executed and is described in connection withFIG. 6. As described above, it should be noted that commit processingmay be initiated at any particular processing point. The commitprocedure ensures that tuples processed by multiple or concurrently runtransactions are returned to a stable state (e.g., from a volatile stateresulting from multiple transactions applied to a given tuple). Forexample, a given tuple may have a column variable changed, e.g., a datecolumn is changed by a date change transaction and a dollar column ischanged by a price adjustment transaction. By way of these transactions,three tuples may exist. For example, a first tuple may be the originaltuple, a second tuple is created by the date change transaction and athird tuple is created by price adjustment transaction. At commit, afourth tuple may be created or one of the three existing tuples may beused to combine changes to the original tuple embodied in the second andthird tuples to generate a final tuple for storage and/or additionalprocessing.

The manner in which mapping module 16 and transaction module 20 committuples (data) from one or more transactions within a database object isdescribed with respect to FIG. 6. Initially, given at step 610, a zoneis in a volatile state with one or more add, modify or delete operationshaving been performed. As previously described, the tuples within a zonemay be in a volatile state (i.e., with pending to uncommittedtransactions) and include added zone descriptors with added columns ofdata, added zone descriptors and added delete tuple identifier columns(i.e., dtid columns).

A database commit function (e.g., for a current transaction) is executedat step 615. The commit function allows for the reconciliation of pluraltransaction with respect to the zone (i.e., the transactions are madepermanent with respect to a given commit transaction). Committransaction processing may operate as follows. The zone index isexclusively locked, thereby preventing a scanner from creating a newlist of zones. Newly created database entries (e.g., added tuples) maybe inserted, e.g., by reference, into the zone index, and for deleteddatabase entries (e.g., deleted tuples), those records may be marked fordeletion, where the commit process may not remove the entries from theindex. One reason the commit process may not remove the entries is thatan active table scan (e.g., from another transaction) may have startedbefore the current commit, and may still need to reference thoseentries. The committing transaction saves its list of entries to deleteand the current scan version number in the zone index structure.

It is determined whether the commit (e.g., for a current transaction)was successful at step 620. Under certain circumstances the databasecannot perform a successful commit. Typically, the transaction or pluraltransactions may contain logical errors or user errors that do notresult in a record that can be made permanent by way of a current commitoperation. Accordingly, the respective transactions cannot be completedand are placed in failed state (e.g., an SQL abort state). When thecommit fails, those affected transactions are rolled back to theirpre-transaction state and an error or other notification may begenerated.

Accordingly, when the commit fails, as determined at step 620, allsecondary zone descriptors and all secondary delete tuple identifiercolumns (dtids′) for all zones in all delete-tuple-sets are freed atstep 630. All added zone descriptors and all added columns of data fromall add-tuple-sets are freed at step 640. In general, when the zonedescriptors are discarded or freed, it means the storage space held bythe data is freed. In the case of a delete transaction, there are twozone descriptors pointing to the same storage spaces for all but thedeleter TID column(s). It is not desirable to free that particularstorage (since there are multiple references (pointers)) until thosereferences can be affirmatively resolved. One example manner handlingthis issue is with reference counting. A physical page of storage can beused by one or more columns in one or more zone descriptors (i.e., apage of data may span multiple zones). Each use of the page is counted.Discarding may be accomplished by decrementing the reference or “use”count. When the count goes to zero, it means that the storage can befreed back for allocation. The failed portion of the commit process endsat step 680.

When the commit is successful, as determined at step 620, the zone mapis updated by adding all zone descriptors from all add-tuple-sets atstep 650. The zone map is further updated by removing all first zonedescriptors and replacing them with all second zone descriptors at step660. All first zone descriptors and first delete tuple identifiercolumns are freed for all zones in the delete-tuple-set at step 670. Thesuccessful portion of the commit process ends at step 680.

At some point in time, the database becomes in need of a clean up (e.g.,similar to disk defragmentation). In other words, there may be storagesegments in need of consolidation or garbage collection. The DBMSmaintains metadata to know whether a given version of a tuple should bevisible to a given transaction. In this regard, each user or processthat initiates a transaction may be given a snapshot of the tuplesaffected by the transaction. That version of tuple may be identified bythe TID or a timestamp. Accordingly, when a database technique such asMVCC is employed, the various transactions may see different versions ofthose tuples. Eventually, after plural transactions, some tuple may nolonger be visible to any transaction and can be garbage collected.

To further illustrate, each executing transaction has a list of TIDs forother transactions whose effects the current transaction cannot “see”(i.e., concurrent transactions or transactions that have not beencommitted). That list of TIDs may be referred to as the “invisibilitylist” or conversely, other TIDs may be considered “visible.”Specifically, the current transaction can test the ctid of a tupleagainst the invisibility list to learn if the tuple was created by atransaction on the invisibility list (i.e., prior to the currenttransaction, yet uncommitted) and that the current transaction shouldnot process “invisible” tuples. For example, given the temporal nexusbetween monotonically incremented TIDs, those transactions with TIDs(e.g., ctids) on the invisibility list have not been committed, andtherefore represent an “unknown” transaction state.

Similarly, the current transaction can test the TID (e.g., dtid) of atuple to learn if the tuple was deleted by a transaction on theinvisibility list and that the current transaction should process thetuple on the invisibility list as if it were “visible.” For example,those transactions that delete tuples prior to the execution of thecurrent transaction represent viable tuples for processing and tuplesthat may be used during the commit process. When tuples are no longervisible based on the invisibility lists, the tuple may be ignored by thecurrent transaction or ultimately may be garbage collected.

It will be appreciated that the embodiments described above andillustrated in the drawings represent only a few of the many ways ofimplementing techniques to delete tuples in a database using a schemewith separate transaction identifier storage.

The environment of the present invention embodiments may include anynumber of computer or other processing systems (e.g., client or end-usersystems, host systems, data servers, etc.) and databases or otherrepositories arranged in any desired fashion, where the presentinvention embodiments may be applied to any desired type of computingenvironment (e.g., cloud computing, client-server, network computing,mainframe, stand-alone systems, etc.). The computer or other processingsystems employed by the present invention embodiments may be implementedby any number of any personal or other type of computer or processingsystem (e.g., desktop, laptop, PDA, mobile devices, etc.), and mayinclude any commercially available operating system and any combinationof commercially available and custom software (e.g., browser software,communications software, server software, mapping module, transactionmodule, etc.). These systems may include any types of monitors and inputdevices (e.g., keyboard, mouse, voice recognition, etc.) to enter and/orview information.

It is to be understood that the software (e.g., mapping module,transaction module, etc.) of the present invention embodiments may beimplemented in any desired computer language and could be developed byone of ordinary skill in the computer arts based on the functionaldescriptions contained in the specification and flow charts illustratedin the drawings. Further, any references herein of software performingvarious functions generally refer to computer systems or processorsperforming those functions under software control. The computer systemsof the present invention embodiments may alternatively be implemented byany type of hardware and/or other processing circuitry.

The various functions of the computer or other processing systems may bedistributed in any manner among any number of software and/or hardwaremodules or units, processing or computer systems and/or circuitry, wherethe computer or processing systems may be disposed locally or remotelyof each other and communicate via any suitable communications medium(e.g., LAN, WAN, intranet, Internet, hardwire, modem connection,wireless, etc.). For example, the functions of the present inventionembodiments may be distributed in any manner among the variousend-user/client, data servers, and host systems, and/or any otherintermediary processing devices. The software and/or algorithmsdescribed above and illustrated in the flow charts may be modified inany manner that accomplishes the functions described herein. Inaddition, the functions in the flow charts or description may beperformed in any order that accomplishes a desired operation.

The software of the present invention embodiments (e.g., mapping module,transaction module, etc.) may be available on a non-transitory computeruseable medium (e.g., magnetic or optical mediums, magneto-opticmediums, floppy diskettes, CD-ROM, DVD, memory devices, etc.) of astationary or portable program product apparatus or device for use withstand-alone systems or systems connected by a network or othercommunications medium.

The communication network may be implemented by any number of any typeof communications network (e.g., LAN, WAN, Internet, intranet, VPN,etc.). The computer or other processing systems of the present inventionembodiments may include any conventional or other communications devicesto communicate over the network via any conventional or other protocols.The computer or other processing systems may utilize any type ofconnection (e.g., wired, wireless, etc.) for access to the network.Local communication media may be implemented by any suitablecommunication media (e.g., local area network (LAN), hardwire, wirelesslink, intranet, etc.).

The system may employ any number of any conventional or other databases,data stores or storage structures (e.g., files, databases, datastructures, data or other repositories, etc.) to store information(e.g., data, documents, zone indices/maps, etc.). The database systemmay be implemented by any number of any conventional or other databases,data stores or storage structures (e.g., files, databases, datastructures or tables, data or other repositories, etc.) to storeinformation (e.g., data, documents, zone indices/maps, etc.). Thedatabase system may be included within or coupled to the server and/orclient systems. The database systems and/or storage structures may beremote from or local to the computer or other processing systems, andmay store any desired data (e.g., data, documents, zone indices/maps,etc.).

The present invention embodiments may employ any number of any type ofuser interface (e.g., Graphical User Interface (GUI), command-line,prompt, etc.) for obtaining or providing information (e.g., databases,documents, indices, range maps, transaction information, etc.), wherethe interface may include any information arranged in any fashion. Theinterface may include any number of any types of input or actuationmechanisms (e.g., buttons, icons, fields, boxes, links, etc.) disposedat any locations to enter/display information and initiate desiredactions via any suitable input devices (e.g., mouse, keyboard, etc.).The interface screens may include any suitable actuators (e.g., links,tabs, etc.) to navigate between the screens in any fashion.

The present invention embodiments are not limited to the specific tasksor algorithms described above, but may be utilized for generating zoneindices or zone maps associated with any type of database, memory or anyother storage structure (e.g., data, zone indices, zone maps,descriptors, ctids, dtids, etc.).

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”,“comprising”, “includes”, “including”, “has”, “have”, “having”, “with”and the like, when used in this specification, specify the presence ofstated features, integers, steps, operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, integers, steps, operations, elements, components,and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

The present invention may be a system, a method, and/or a computerprogram product. The computer program product may include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out aspects of thepresent invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

What is claimed is:
 1. A method comprising: partitioning, via a hardware processor, a multi-version concurrency control database to store a database object in a form of a database table as a plurality of different zones, wherein each of the plurality of different zones comprises a set of data including plural copies of data tuples of the database table and each copy of a data tuple of the database table includes a corresponding change to data of that data tuple of the database table and is associated with a unique identifier upon creation, wherein the plural copies of the data tuples of the database table are stored until the corresponding changes to the data of the data tuples of the database table in the plural copies are reconciled and committed, wherein each copy of a data tuple of the database table is associated with a transaction identifier of a database transaction generating the corresponding change to data for that data tuple of the database table, wherein each transaction identifier corresponds to a timestamp of the corresponding change and includes a counter associated with the changes to data for the associated data tuple of the database table, wherein each zone is associated with a unique zone identifier, and wherein the zone identifier is associated with unique version numbers for the plural copies of data tuples; and for each of the plurality of different zones within the database table, performing via the hardware processor: scanning the set of data located within the zone to identify one or more transactions to delete one or more data tuples located within the zone; storing the transaction identifiers associated with the one or more identified transactions in an allocated storage space separate from the set of data located within the zone, wherein the transaction identifier is uniquely associated with the one or more data tuples deleted by the one or more identified transactions and indicates visibility of the copies of the data tuples to other transactions; generating a map structure indicating storage of the set of data located within the zone and the allocated storage space of the transaction identifiers associated with each of the one or more identified transactions, wherein the map structure includes a zone index associated with the zone and a first zone descriptor including a first set of pointers to the data tuples located within the zone and to the allocated storage space of the transaction identifiers of the one or more identified transactions, and wherein the zone index maps the zone identifier associated with the zone to the first zone descriptor; updating the transaction identifiers in response to receiving a current transaction to delete one or more data tuples located within the zone, wherein updating the transaction identifiers includes: generating one or more transaction identifiers uniquely associated with the one or more data tuples deleted by the current transaction and corresponding to a time of deletion of the one or more data tuples and storing the one or more transaction identifiers associated with the current transaction within a new storage space such that the one or more transaction identifiers associated with the current transaction is stored separately from the allocated storage space of the transaction identifiers of the one or more identified transactions; generating a second zone descriptor associated with the zone within the map structure including the first set of pointers with a pointer to the new storage space for the updated transaction identifiers in place of a pointer to the allocated storage space of the transaction identifiers of the one or more identified transactions; and replacing the first zone descriptor with the generated second zone descriptor associated with the zone within the map structure, wherein the storage of the updated transaction identifiers in the new storage space facilitates compression of the updated transaction identifiers, and wherein the zone index allows scanners to operate without synchronizing access to data.
 2. The method of claim 1, wherein updating the transaction identifiers renders portions of the set of data created by concurrently executing transactions invisible to the one or more identified transactions and renders portions of the set of data deleted by concurrently executing transactions visible to the one or more identified transactions based on transaction identifiers for the concurrently executing transactions.
 3. The method of claim 1, wherein replacing the first zone descriptor includes: replacing the first zone descriptor with the generated second zone descriptor within the map structure in response to the current transaction being committed.
 4. The method of claim 1, further comprising: rolling back the transaction to the set of data by discarding the second zone descriptor and deallocating the new storage space for the updated transaction identifiers.
 5. The method of claim 1, further comprising: storing the updated transaction identifiers in a contiguous storage space and compressing the updated transaction identifiers.
 6. The method of claim 1, wherein: when one or more transactions creates one or more data tuples located within the zone, the transaction identifier is assigned as a creator identifier; and when one or more transactions modifies one or more data tuples located within the zone, the transaction identifier is assigned as a deleter identifier.
 7. The method of claim 1, wherein each of the plurality of different zones includes metadata describing the one or more data tuples located within the zone. 